1. Field of the Invention
The present invention relates to a method for producing an inkjet head by laminating two units having different thermal expansion coefficients to each other and the inkjet head.
2. Description of the Related Art
An inkjet head produced by laminating a flow path unit and an actuator unit to each other has been described in JP-A-2003-237078 (FIGS. 1 to 4). Ink flow paths having nozzles and pressure chambers respectively are formed in the flow path unit. The actuator unit has a size covering the pressure chambers. The actuator unit includes a plurality of piezoelectric ceramic sheets, which are electric insulators. Some of the piezoelectric ceramic sheets are sandwiched between electrodes disposed on opposite sides. In a process of production, the portion of the piezoelectric ceramic sheets sandwiched between the electrodes serves as a polarized active portion, when a high voltage is applied there to. In the actuator unit, such active portions are formed for the pressure chambers respectively. When the two electrodes on opposite sides of each active portion are made different electric potentials, the active portion stretches in the direction of the thickness of each sheet. When pressure is applied on ink in the pressure chamber because of reduction in volume of the pressure chamber due to the stretching of the active portion, ink is jetted from the nozzle communicating with the pressure chamber. In this type inkjet head, a large number of electrodes can be arranged densely on each piezoelectric ceramic sheet because the piezoelectric ceramic sheet has a size covering the plurality of pressure chambers. For this reason, pressure chambers can be arranged so densely as to face electrodes respectively, so that high-resolution printing can be achieved.
Each active portion and two electrodes on opposite sides of the active portion form a capacitor. As the capacitance of the active portion increases, the amount of expansion/contraction of the active portion increases. Accordingly, as the capacitance of the active portion increases, the speed of ink jetted from a nozzle corresponding to the active portion increases.
In the aforementioned inkjet head, the flow path unit and the actuator unit are generally laminated each other by an adhesive agent. In the existing situation, a heat-curable adhesive agent is used as the adhesive agent because it is excellent in ink resistance, short in curing time and small in variation of thickness after curing due to low viscosity just before bonding.